Dynamoelectric machine cooling and brush lubrication



Aug. 12, 1952 FlsHER 7 2,606,946

DYNAMOELECTRIC MACHINE COOLING AND BRUSH LUBRICATION FiledJuly 19, 1950y 3Sheets-Sheet 1 Inventor-.- Q Alec Fisher,

l-lis At'l: ofney.

Aug. 12, 1952 A. FISHER 2,606,946

DYNAMOELECTRIC MACHINE COOLING AND BRUSH LUBRICATION Filed July 19, 19503 Sheets-Sheet 2 Inventor: Alec Fisher,

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H is Att rney.

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His At't Orney Patented Aug. 12 1952 DYNAMOELECTRIC MACHINE COOLING ANDBRUSH LUBRICATION Alec Fisher, Lynn, Mass., assignor to General ElectricCompany, a corporation of New York Application July 19, 1950, Serial No.174,650

9 Claims. 1

My invention relates to dynamo electric machines and has particularsignificance in connection with an aircraft generator for a high flyingairplane.

Heretofore, the electrical systems of airplanes adapted for highaltitude operation have presented vexatious problems-because excessiveheating of all parts, and excessive commutator brush wear, is found tooccur at-the low air densities and low relative humidities existing athigh atlitudes. Brush wear, heating and other high altitude problems arenot so serious in the-case of most motors used in theelectricalsystem,because they operate only intermittently (such as toadjust wing flaps) but are a considerable problem in connection with theprincipal generator of the system because it must operate continuouslyand usually under load conditions.-

lhe answer lies not merely in pressurizing or I supercharging thedynamoelectric machine or collector enclosure,- for the problem is notmerely that of a rarified atmosphere but is that of adry atmosphere. Forexample, if the machine was pressurized with the sea level atmosphere ofthe arctic 'region'on a coldwinter day, there would not be anywhere nearthe requisite moisture to assure proper commutation.

Furthermore, heat dissipation problems are accentuated at modernsupersonic speeds because the temperature of the air available forcooling is, because of the heat generated upon-impact, often higher thanthe allowable temperature for the generator. v i

It is an object of the present invention to provide simple means forovercoming the abovementioneddifiiculties.

Itis a further object of the present invention to provide a liquidfilled generator and intercooler systemtogether with means forpreventing or minimizing generator brush wear, particularly with highaltitude operation and without departing from standard brushmanufacturing techniques. I

Broadly the means employed in the embodiments herein illustratedanddescribed comprise a direct current generator for a high flyingairplane in which the interior of the generator is submergedin asuitable liquid which is cooled in a separate intercooler" so that theliquid acts to efiectively cool the electrical parts of the machine, andmeanwhile the commutator and brushes are sealed in a somewhat separateenclosure and means are provided for pumpinga major portion of theentrapped fluid out of this somewhat; separateenclosure to maintainproper vapor pressure in the collector housing, thereby to permit goodcontact between brush and commutator and at the same time preventdusting away of the brushes.

Other objects and advantages will become apparent and my invention willbe better understood from consideration of the following descriptiontaken in connection with the accompanying drawing in which Fig. i is anelevational view (partly in section) of a totally enclosed aircraftgenerator with a suitable liquid entrapped therein, thereby to provideadequate cooling and brush protection at substantially any altitude;Fig. 2 is a seetionalview of a modification showing means for keeping amajor portion of the entrapped fluid out of the somewhat separatecommutator enclosure; Fig. 3 is a cross-sectional view taken alongtheline 3-3 of Fig. 2; and Fig. 4 is a partial sectional view of anothermodification.

In Fig. 1 I have shown a dynamo electric machine such as an aircraftgenerator adapted to be driven by a source of mechanical power such as agasoline engine or jet engine (not shown) driving a splined-end II of agenerator shaft I 2. Shaft I2 drives a laminated rotor core portion l3which is arranged to react electrodynamically with a stator corecomprising salient field poles l4 joined by a yoke or outer frame l5.Field excitation is supplied through field coils IS on poles l4 and therotor I3 is provided with a conventional armature winding l1 and, ifdesired, axially extending rotor core ventilatingpassages Hi. In more orless conventional manner the armature winding llis connected at tappedintervals such as through risers H) to the individual segments 20 of themachine commutator which is arranged to be driven by the shaft l2 as isanaxial flow impeller 21. If desired the commutator risers 19 may beradially spaced from each other so that the ventilating and commutatorlubricating/fluid may flow from over the commutator and between thebrush sets indicated at 22-, between the risers and into the ventilatingpassages l8'as wellas into the gap between rotor and stator and betweenthe field coils IS.

Th entire machine is arranged to be liquidtight and to this end it isprovided with substantially solid end flanges 23 and 24. Inorder toassure the removal from the core l3 of heat which may be generatedtherein by eddy currents and by electric current flowing through thearmature winding l1, andalso-in order to insure suitable commutation ashereinafter more fully explained, the entire interior of 'the'machin issubmerged in a suitable liquid 25 which is driven axially through themachine by the impeller 2I and out of the machine adjacent the endshield 23 through a conduit 26 and then through an intercooler or heatexchanger 21 and through a conduit 28 back through the other end shield22 and then back into the fan 2i. A number of liquids are suitable forthis application, for example, ethylene glycol or diethylene glycol(sometimes known as Prestone or Zerex), halogenated diphenyl (sometimesknown as Pyranol) tributyl phosphate, liquid organopolysiloxanes orother silicone oils. actually been used by applicant and found to givegood results. The liquid should of course have some insulatingproperties, be non-arcing and non-carbonizing and must not congeal attemperatures apt to be encountered in operation. My invention is not,however, limited to a case where a single type of oil or other liquid isused, but obviously includes a mixture of liquids, for example, amixture of one selected for its heat conductivity characteristics andanother selected for its good vapor characteristics for high altitudebrush operation. This liquid is cooled in the intercooler by passingtherethrough a separate liquid or gas schematically illustrated byarrows 29 as entering and leaving the intercooler by a separate conduit30. While at supersonic speeds, air having the impact velocity of theaircraft or other vehicle might not be suitable for this intercoolercooling application, air blast means independent of vehicle speed may beprovided, or other fluids may be used, for example, liquid fuel on itsway to the aircraft prime mover engine may be passed through conduit 29with the consequent advantage that little of the heat is lost to theoverall system.

With the arrangement 'justdescribed, cooling of the machine may beadequately taken care of regardless of vehicle speed and, at the sametime, means are provided for continually lubricating and wetting thecommutator so that the brushes do not rapidly dust away. In order toreduce the rotational losses it is in many cases desirable to fill witha resinous or other composition the interstices between the rotorwinding elements (and, possibly, between the stator field windings aswell) so that there will be no interrupted surfaces presented to thefiuidby these members. 7

Of course, the different brush sets and also the diiferent commutatorsegments are operating at different potentials and, therefore, asalready indicated, the liquid must be an insulator, at least to someextent, yet it must have a thin enough film thickness to allow eachbrush to make contact with the commutator or else the actual filmthickness must in some manner be reduced as by allowing only a vapor ofthe liquid to contact brushes and commutator. Thus, in order to assurethat the brushes will be in very intimate contact with the commutator,it may be found desirable to exclude a major portion of the fluid fromthe brushes and commutator as is possible with the embodiments shown inFigs. 2,3 and 4. As seen in Fig. 2, a shaft H2 is adapted to drive arotor core portion H3 cooperating with salient stator poles H4 securedtoan outer yoke which forms a portion of a fluid-tight case H5. Thefield poles are provided with field exciting windings H6 and the rotoris provided with an armature winding I I! connected through commutatorears or risers H9 to commutator segments I28. Commutator segments I20are contacted by Even ordinary engine oil has brushes I3I secured inbrushholders I22 with a 4 conventional spiral spring I32 (see Fig. 3)exerting pressure lengthwise of each brush to cause it to closelycontact the commutator.

In Fig. 2 an impeller I2I is shown at the end of the machine oppositethe commutator end. The interior of the machine is submerged in asuitable liquid I25 which is forced by the impeller through and aroundthemachinewindings and out a conduit I26fto an intercooler I2'I and thenback to the other end ofth'e machine through a conduit I28. In theintercooler a conduit system I129 provides a heat exchanging path for anintercooling medium.

With the arrangement shown in Figs. 2 and 3 (and also with the modifiedarrangement shown in Fig. 4 as hereinafter explained) provision is madeto allow sufficient liquid or vapor of the liquid to surroundthecommutator and brushes to prevent brush dusting for requisite highaltitude performance, while too must liquid is prevented frominterfering with the contact between commutator and brushes byenclosingthe commutator and brush sets in a somewhat separate enclosure andproviding means to pump oil out of this enclosure or enclosures. Thus,with a substantiallycomplete enclosure about the commutator as providedby an annular member I33 as shown in Figs. 2 and 3, the radiallyextending, circumferentially spaced, individual commutator ears H9 (orextensions II'Ia of the armature winding ends axially beyond thecommutator ears) are adapted to act as pumping vanes to pump oil awayfrom the commutator without materially affecting the flow of liquid inthe remainder of the machine. Alternatively (or, as shown, additionally)other means can be provided to pump out the commutator enclosure such asby utilizing the well known tapered-cylindrical gap principle to providea pumping action. Thus in Fig. 2 I have shownjgreatly exaggerated, atapered gap between the commutator surface and the adjacent innerperiphery I34 of the brush and commutator enclosing annular block I33which is also provided with four pockets I35 for housing the individualbrush sets. If desired, the top of the brushes can be made accessible bysealing the pockets I35 with removable caps I36 which can be removed toallow assembly of, and access to, the brushes, brushholders and brushpressure springs. Y

If desired, there may be added (as shown in Fig. 2) a pipe I31 leadingfrom the outside air into the machine and containing a one-way valve I38so that when the generator has initially started up (presumably at lowaltitude although with the invention the ambient humidity is actually oflittle importance since sufficient vapor for proper lubrication of thecollector willbe provided by the liquid), outside air can enter theenclosure within block I32 when the liquid is first drawn out bywhatever pumpaction is provided.

In Fig. 4 I have'shown a modification in which a machine shaft 2 I 2extends through an enclosing casing 2I5 with a close seal beingformed byan annular sealing ring 240 between shaft and housing to take the placeof the one-way valve indicated in Fig. 2. In Fig. 4, a commutator andbrush set enclosing housing 233 makesa tapered clearance with acommutator .220 and at the outer end of this tapered clearance, arunning seal is provided between commutator and housing by anannularring 24I designed to provide a regulated leakage at this'point.When the machine of Fig. 4' is stopped, the running sealprovidedby'packing 241: will prevent the liquid. 225 from vrunningzlbackinto the commutator enclosure. Excess liquid may be drained off andreturned'to the system by a one-way valve 242 and ambient air may enterpast seal 240, but at all times sufficient liquid will have passedthrough the commutator enclosure to provide sufiicient vapor for aproper brush lubrication film, or at least it lies within the provinceof the designer ordinarily skilled in the art to so design the parts asto accomplish this result.

I do not intend that my invention shall be considered limited to theconstructions illustrated and described, as it obviously includes theprovision of othermeans for pumping out the somewhat separate enclosurefor commutator and brushes, as by providing spiral grooves upon thecommutator surface.

The cylinder placed around the commutator in the illustrated embodimentsof Figs. 2, 3, and 4 serves to reduce turbulence around commutator andbrushes, especially since liquid has been pumped out of the somewhatseparate chamber at these points, and with armature and statorcompletely smoothed out at the so-called air gap, the rotational lossesbecome merely the equivalent of that obtained in a long, cylindricalbearing, or in other words very low indeed.

Among the advantages of using a liquid rather than a gas for the instantapplication is that a liquid can be made to more quickly give up itsheat in an intercooler and more quickly take heat out of the machineparts to be cooled and there is the additional fact that it would bevery difiicult to find a gas which would be suitable both for coolingand for acting as a lubricant which will allow satisfactory highaltitude commutation.

The liquid-fill d commutator type machine used with an intercoolersystem is adapted to provide constant environmental conditions both tofacilitate the cooling of the machine (and incidentally eliminateconventional complicated air blast pipes) and also to prevent or leastmaterially reduce brush wear at altitudes, of, for example, more thanthree miles above sea level. With either the embodiment of Fig. 1 orthat of Figs. 2 and 3, the liquid acts as an insulator for the windingsas well as a very efficient cooling medium for the machine andlubricating medium. for the commutator. However, the non-arcing and filmthickness properties of the liquid become of less importance when anarrangement is used, such as is suggested by Figs. 2 and 3, for pumpinga substantial portion of the liquid out of a somewhat separatecommutation chamber wherein the liquid has nevertheless been allowed tovaporize sufiiciently to prevent brush dusting at high altitudes.

There is thus provided a device of the character described capable ofmeeting the objects hereinabove set forth and, for example, allowingefficient dynamoelectric machine cooling at supersonic speeds whileproviding adequate brush protection at altitudes above three miles high.

While I have illustrated and described particular embodiments of myinvention, modifications thereof will occur to those skilled in the art.I desire it to be understood, therefore, that my invention is not to belimited to the particular arrangements disclosed and I intend in theappended claims to cover all modifications which do not depart from thespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

,6I-..-;.- ,1. For a commutator type dynamoelectricmachine adapted tooperate on an aircraft adapted to. fiy, atsupersonic speeds :at' highaltitude and in a. rarified qatmosphere, ,.the.-;combination of acommutator, commutator brushes, an enclosing casing for said machine, anintercooler located outside of said casing, ducts connecting saidmachine in said casing with said intercooler, intercooler cooling means,a substantially separate enclosure for said brushes .and commutator withsaid substantially separate enclosure being located interiorly of saidfirst casing, a liquid in said casing,. insaid ducts and in the portionof said intercooler connected to said ducts, and means fonpumping aportion of said liquid out of said substantially separate enclosure forsaid commutator and brushes, whereby said machine may be readily cooledby said liquid and said brush life enhanced regardless of altitude whilesaid liquid is substantially prevented from interfering with the desiredelectrical contact between said commutator and brushes.

2. For a commutator type dynamoelectric machine adapted to operate on anaircraft adapted to fly at supersonic speeds in a rarified atmosphere,the combination of a commutator, commutator brushes, an enclosing casingfor said machine, an intercooler located outside of said casing, ductsconnecting said machine in said casing with said intercooler,intercooler cooling means, a substantially separate enclosure for saidbrushes and commutator with said substantially separate enclosure beinglocated interiorly of said first casing, a liquid in said first casing,in said ducts and in the portion of said intercooler connected to saidducts, means for pumping a portion of said liquid out of saidsubstantially separate enclosure for said commutator and brushes, andone way valve means for introducing atmosphere to said separateenclosure to displace said liquid, whereby said machine may be readilycooled by a liquid which will not interfere with commutation but isadapted to provide a vapor to moisturize the atmosphere surrounding saidcommutator and brushes and thereby enhance commutation.

3. The combination for operation at a high altitude, of a totallyenclosed aircraft generator having a stator core portion comprisingsalient field poles and windings, a rotor core portion having anarmature winding, a commutator connected to said armature winding andaxially spaced from said core portions, a plurality of brushescontacting said commutator, a compound filling the interstices betweensaid salient field pole windings to present a smooth inner periphery, acompound filling the interstices between elements of said armaturewinding and rotor core to present a smooth outer periphery, wallsdefining a separate enclosure for said commutator and brushes with saidseparate enclosure being located completely within the main enclosure ofsaid generator, an intercooler arranged separate from said generator,pipes connecting opposite ends of said generator with said intercooler,a mixed liquid completely submerging said stator and rotor core portionsand filling said pipes and an associated portion of said intercooler,said mixed liquid comprising a mixture of a first liquid having heatconductivity characteristics and a second liquid having vaporizationcharacteristics to provide a brush life enhancing vapor, and means forpumping a substantial portion of said mixed liquid out of said separateenclosure for said commutator and brushes whereby said liquid will notflood said separate enclosure and prevent good electrical contactbetween said commutator and brushes.

4. The combination as in claim 3 further characterized by said means forpumping comprising radially extending, circumferentially spaced apartcommutator risers joining said armature windin and said commutator.

5.. The combination as in claim 3 further characterized by saidcommutator comprising commutator ears and said pumping means includingpumping vanes arranged adjacent the ends of said ears.

6. The combination as in claim 3 further characterized by said means forpumping comprising a configuration of said walls defining said separateenclosure to form with said commutator a wedge shape clearanceextendingaxially of said machine with the mouth of the Wedge located at the endof said commutator adjacent said stator and rotor core portions.

7. A high altitude rotating machine for use aboard aircraft, saidmachine having a current collecting assembly comprising a commutator andbrushes, said machine having a liquid tight casing enclosing all of theinterior of said machine, and said machine having an annular memberlocated interiorly of said casing and defining a separate enclosureenclosing said current collecting assembly including said brushes,machine ventilating means for causing ventilating liquid to circulatethrough said machine, and means for exhausting said liquid from saidseparate enclosure enclosing said current collecting assembly.

8. .A rotaryelectric machine comprising magnetic elements, a commutator,a plurality of brushes contacting said commuator, a liquid tight casingforming an outer chamber within which said magnetic elements, saidcommutator and said brushes are "enclosed, enclosure meansdefining aninner chamber within which said commutator and brushes are furtherenclosed, a liquid filling the outer chamber to a point above saidmagnetic elements, passage means for establishing communication betweensaid inner and outer chambers to allow a portion of said liquid to entersaid inner chamber, and means for introducing a gas into said innerchamber to prevent said liquid from submerging said commutator andbrushes.

9. The invention as defined in claim 8 in combination with anintercooler heat exchanger heated outside of said machine casing andconnected thereto to cool said liquid.

ALEC FISHER.

REFERENCES CITED The following references are of record in the file ofthisppatent:

UNITED STATES PATENTS Number Name Date 837,033 Bunet Nov. 27, 1906931,448 Mattman Aug. 17, 1909 1,443,644 Nobuhara Jan. 30, 1923*1,531,724 "Arutunofi Mar. 3 1, 1925 1,938,077 Lysholm Dec. 5, 193BFOREIGN PATENTS Number Country Date 170,946 Great Britain Oct. 31, 1921204,123 Great Britain Sept. 21,1923 559,354 France June 14, 1923

